Prompt caching broken for GPT 5.4 and 5.5

Hi,

I got an email notification from OpenAI status page (in early hours for me). So I don’t know for sure, but this might be related to the recent OpenAI status incident with elevated 431 errors across API components. Since Chat Completions and Responses were among the affected components, it could have impacted request handling around the same time. The status page says it’s resolved now, so if caching is still missing after recovery, it may be a separate issue.

OpenAI Status

Elevated 431 Errors - OpenAI Status

All impacted services have now fully recovered.